This invention relates to a capacitive linear or rotary transmitter for controlling and positioning displaced objects by measuring the displacement, angle or speed of the displaced object, which in one embodiment as a rotary transmitter is formed by two mutually opposed stators defining a reciprocal spacing, the gap of which has rotatably arranged in it a rotor which is rotatably coupled to a spindle coupled to the displaced object, a first air gap (measurement air gap) being formed between one stator and the rotor, and a second air gap (decoupling or balancing air gap) being formed between the other stator and the rotor, with electrically conductive coatings situated in each case on mutually confronting sides of the stators and of the rotor which together with the associated air gap form capacitors in each case, the capacitance value of which varies with the rotation of the rotor.
A rotary transmitter of this nature has been disclosed, for example in U.S. Pat. No. 4,238,781. A disadvantage of this known rotary transmitter consists in that a phase displacement of an output signal is evaluated as a function of the angle of rotation which leads to a comparatively complex evaluator circuit which has little precision. This known rotary transmitter is a transmitter for application in an electricity meter which is to be utilised to read the current consumption in households and which merely serves the purpose of drawing a distinction between ten digits and of producing these in digital form at an output means.
A rotary transmitter of this kind is consequently unsuitable for high-precision positioning particularly of machine elements on machine tools, in which it is essential to differentiate within the range of fractions of minutes of angle. As for the rest, the U.S. Pat. No. 4,238,781 does not disclose any precisely sinusoidal capacitance graph for the coupling capacitors, because the coverage density of the coatings on the one stator over the angle of rotation lacks the configuration required for this purpose. This restricts the obtainable precision. Beyond this factor, the condition applies in respect of the coatings on the rotor, that these cannot generate two sinusoidal halfwaves because they do not extend along an angle of rotation of 180.degree.. The obtainable precision is impaired additionally, thereby.
The invention consequently has as its fundamental object to develop a rotary transmitter of the kind defined in the foregoing in such manner that it has a substantially improved resolution with superior precision and reduced complexity of the circuitry.